At least five percent of the internet’s top 100,000 websites are using a new kind of online tracking system – one which essentially takes a “fingerprint” of your computer via its web browser.

What’s more, the
software – known as canvas fingerprinting – is nearly impossible
to block using conventional privacy tools.

According to a new report by ProPublica, the curtains over canvas
fingerprinting will officially be lifted in a forthcoming paper
authored by researchers at Princeton University and Belgium’s KU
Leuven University.

Here’s how it works: When you visit a website that features such
tracking technology, the site asks your browser to “draw a
hidden image.” Since every computer renders the image in a
different way, that drawing is used to label your device with a
unique number that allows trackers to keep an eye on your
browsing activity across the internet.

Although there is more than one type of canvas fingerprinting,
the most widely used software is developed by AddThis, and is
reportedly used on popular websites like Whitehouse.gov, online
dating site PlentyOfFish, CBS, and even YouPorn (a list of known
sites using the software can be found here).

An AddThis spokesperson also said that it did not inform the
websites in question when it put its tracking technology in
place. After ProPublica’s original article was published, a
YouPorn spokesperson said the website was unaware the app was
tracking users and has removed AddThis functionality.

AddThis chief executive Rich Harris stressed that the company
does not use canvas fingerprinting for anything other than ad
targeting and personalization, and that users can stop their data
from being used for advertising or marketing by installing a
specific opt-out cookie on their computers. This would not
stop AddThis from collecting data, however; it would simply stop
them from using it to custom-tailor ads for you.

The company also said it does not use any data it gathers from
government websites. So far, it claims to have only used data for
“internal research and development.”

Still, the fact that all users have to rely on is a promise from
AddThis “is not the best privacy assurance,” said
Princeton computer science professor Arvind Narayanan, who helped
lead the research team responsible for uncovering the system.

If opting out is not a satisfactory option on its own, you’re
left with a few different possibilities. You could download the
Tor
browser, which helps users avoid numerous types of online
tracking, or you could block JavaScript from loading in your
browser, which ProPublica notes could make many websites not work
properly.

There’s also a browser in the works called Chameleon, which is specifically designed to block
fingerprinting, but at this stage is only recommended for
“tech-savvy users.”

AddThis is reportedly contemplating ending its test of the
tracking tech soon because "it's not uniquely identifying
enough."